Semiconductor filter circuit and method

Abstract

A filter circuit ( 10 ) is formed on a semiconductor substrate ( 11 ) formed with a trench ( 40 ) that is lined with a dielectric layer ( 38 ). A conductive material ( 37 ) is disposed in the trench and coupled to a node ( 62 ) to provide a capacitance that modifies a frequency response of an input signal (V IN ) to produce a filtered signal (V OUT ). An electrostatic discharge device includes an inductor ( 74 ) coupled to back to back diodes ( 17, 18 ) formed in the substrate to avalanche when a voltage on the node reaches a predetermined magnitude.

1. An integrated filter for filtering an input signal, comprising:
 a semiconductor substrate formed with a trench that is lined with a dielectric layer;  
 a first conductive material disposed in the trench and coupled to a node to provide a capacitance that modifies a frequency response of the input signal to produce a filtered signal;  
 a protection circuit that includes back to back diodes formed in the semiconductor substrate to avalanche when a voltage on the node reaches a predetermined magnitude; and  
 an inductor formed oven in the semiconductor substrate with the inductor coupled between the node and an input that is configured to receive an input signal to the integrated filter.  
 
   
   
     2. The integrated filter of  claim 1 , wherein the inductor is formed as a planar device on a surface of the semiconductor substrate. 
   
   
     3. The integrated filter of  claim 1 , wherein the semiconductor substrate includes a base layer of a first conductivity type and a doping concentration in a range between 10 18  and 10 21  atoms per cubic centimeter. 
   
   
     4. The integrated filter of  claim 3 , wherein the back to back diodes include:
 a first doped region of a second conductivity type that forms a first junction with the base layer; and  
 a second doped region having the first conductivity type for forming a second junction with the first doped region, wherein the second doped region is coupled to the node.  
 
   
   
     5. The integrated filter of  claim 4 , wherein the first doped region comprises an epitaxial layer grown on the base layer. 
   
   
     6. The integrated filter of  claim 5 , wherein the second doped region is diffused from a surface of the epitaxial layer. 
   
   
     7. The integrated filter of  claim 6 , wherein the second doped region includes:
 a first portion having a first surface concentration and diffused to a first depth; and  
 a second portion having a second surface concentration less than the first surface concentration and diffused to a second depth greater than the first depth.  
 
   
   
     8. The integrated filter of  claim 5 , wherein the epitaxial layer includes:
 a first portion formed over the base layer and having a first doping concentration; and  
 a second portion formed over the first portion and having a second doping concentration less than the first doping concentration.  
 
   
   
     9. The integrated filter of  claim 5 , wherein the epitaxial layer has a thickness between two and ten micrometers and a doping concentration in a range between 10 16  and 10 18  atoms per cubic centimeter. 
   
   
     10. The integrated filter of  claim 5 , wherein impurities of the first conductivity type are diffused through a surface of the epitaxial layer to reduce a doping concentration of the epitaxial layer within a depth less than three micrometers. 
   
   
     11. The integrated filter of  claim 1 , wherein the semiconductor substrate includes a base layer having a doping concentration in a range between 10 12  and 10 14  atoms per cubic centimeter. 
   
   
     12. The integrated filter of  claim 1 , wherein the trench is formed in a first well region of the semiconductor substrate. 
   
   
     13. The integrated filter of  claim 12 , wherein the back to back diodes are formed in a second well region of the semiconductor substrate, the second well region and the semiconductor substrate having the opposite conductivity type. 
   
   
     14. The integrated filter of  claim 13 , wherein the back to back diodes further comprise:
 a first doped region formed within the second well region to provide a first junction of the back to back diodes; and  
 a second doped region formed within the second well region to provide a second junction of the back to back diodes.  
 
   
   
     15. The integrated filter of  claim 1 , wherein the first conductive material comprises doped polysilicon. 
   
   
     16. The integrated filter of  claim 1 , wherein the capacitance is produced by a trench capacitor, further comprising a thin film resistor coupled to the trench capacitor. 
   
   
     17. The integrated filter of  claim 1  wherein the dielectric material is formed within the trench. 
   
   
     18. A wireless communications device, comprising:
 a power stage that receives a modulated signal and transmits an output signal of the wireless communications device;  
 a modulator that modulates a radio frequency carrier signal with an audio signal to produce the modulated signal;  
 a microphone for converting voice information to the audio signal, where the microphone receives a portion of the output signal; and  
 a filter formed on a semiconductor substrate and interposed between the microphone and the power stage for attenuating radio frequency components of the output signal, including 
 a first doped region formed on a surface of the semiconductor substrate;  
 a second doped region formed on the surface of the semiconductor substrate, the second doped region having a conductivity opposite to a conductivity of the semiconductor substrate;  
 a trench formed within the first doped region, the trench having sidewalls;  
 a dielectric material positioned at least on a portion of the sidewalls of the trench to line the trench;  
 a first conductive material disposed on the dielectric material within the trench to provide a capacitance that attenuates the radio frequency components; and 
 an electrostatic discharge circuit including back to back diodes formed in the second doped region to limit an amplitude of a terminal voltage of the filter to a predetermined value.  
 
 
 
   
   
     19. An integrated filter for filtering an input signal, comprising:
 a semiconductor substrate;  
 a first doped region formed in the semiconductor substrate;  
 a second doped region formed in the semiconductor substrate;  
 a trench formed in the first doped region wherein the trench is lined with a dielectric layer;  
 a first conductive material disposed in the trench and coupled to a node to provide a capacitance that modifies a frequency response of the input signal to produce a filtered signal; and  
 a protection circuit that includes back to back diodes formed in the Second doped region to avalanche when a voltage on the node reaches a predetermined magnitude.